The background of the present invention is described herein in the context of pay television systems, such as cable television and direct broadcast satellite (DBS) systems, that distribute a variety of program services to subscribers, but the invention is by no means limited thereto.
In the pay television industry, "programmers" produce "programs" for distribution to various remote locations. A "program" is a collection of related services, including but not limited to video, audio, closed-captioning and teletext services. A single programmer may wish to supply a variety of such services. Typically, a programmer will supply these services via satellite to individual subscribers (i.e., DBS subscribers and/or cable television operators). In the case of cable television operators, the services transmitted via satellite are received at the operator's "cable head-end" installations. A cable operator typically receives programs and other services from many programmers and then distributes them to its subscribers. In addition, a cable operator may insert locally produced services at the cable head-end. The selected services and locally produced services are then transmitted to the individual subscribers via a coaxial cable distribution network. In the case of the DBS subscribers, each subscriber is capable of receiving a satellite down-link from the programmers directly.
In the past, pay television systems, including cable and DBS systems, have operated in the analog domain. Recently, however, the pay television industry has begun to move toward all digital systems wherein prior to transmission, all analog signals are converted to digital signals. Digital signal transmission offers the advantage that digital data can be processed at both the transmission and reception ends to improve picture quality. In addition, digital data compression techniques have been developed that achieve high signal compression ratios. Digital compression allows a larger number of individual services to be transmitted within a fixed bandwidth. Bandwidth limitations are imposed by both satellite transponders and coaxial cable distribution networks, and therefore, digital compression is extremely advantageous.
In addition, there is a growing trend toward a merger of the previously separate technologies of telecommunications including voice and data telecommunications and television including satellite, broadcast and cable television. There has emerged an increased interest in developing adaptable transmission systems capable of handling any one or more of a collection or plurality of such services. The primary media investigated for providing such services to data comprise, for example, coaxial cable, land-based microwave, so-called cellular radio, broadcast FM, broadcast satellite and optical fiber, to name a few. It is desirable that the decoder in such adaptable transmission systems be flexible so that a subscriber can easily arrange the decoder to accept those services selected by the subscriber.
Each media has its own characteristics. For example, comparing cable and satellite for digital data transmission, cable tends to have a medium error rate, but when errors appear, the errors come in long bursts. Satellite as a media has a fairly poor error rate, primarily due to the requisite weak signal power, and hence, low signal to noise ratio. In satellite, then, the poor error rate is specially corrected utilizing such techniques as convolutional error correctors, not required in a cable environment.
In copending U.S. application Ser. No. 07/968,846, filed Oct. 30, 1992 and entitled "System and Method for Transmitting a Plurality of Digital Services," now U.S. Pat. No. 5,400,401 there is described an encoder for generating a multiplexed data stream carrying services to remote locations via, for example, a satellite or a cable distribution network. The generated data stream comprises a continuous sequence of frames, each frame comprising two fields, and each field comprising a plurality of lines. A first group of lines of a field defines a transport layer and a second group of line defines a service data region. A feature of the disclosed scheme is the ability to dynamically vary the multiplexed data stream from field to field. Another feature of the disclosed scheme is that the data transmission rate of the multiplexed data stream is related to the frequency of known analog video formats, i.e. frame, field and horizontal line rates.
The multiplex data stream generated by the encoder is transmitted to a plurality of remote locations. Each of the remote locations is provided with a decoder for receiving a multiplex data stream and extracting selected services therefrom. A block diagram of such a decoder 280 is shown in FIG. 1. Video services, for example, may be extracted from the multiplex data stream 288 and displayed on a display device 306 at the remote location. In greater detail, the decoder receives successive fields of the multiplex data stream and, for each field, extracts a multiplex map from the field to determine the content of the transport layer region of that field. With the multiplex map, the decoder 280 is able to extract the system data packets and the multiplex control packet from the transport layer region. In response to a user service selection 296, the decoder 280 examines the multiplex control packet for each field to determine which portion of the service data region of that field is allocated to the selected service. Once the correct portion has been identified, the decoder 280 is able to extract the selected service data from that field. As shown in FIG. 1, the decoder described in copending U.S. application Ser. No. 07/968,846 now U.S. Pat. No. 5,400,401 is capable of extracting only four audio services or channels at a time. In addition, the decoder of FIG. 1 is also limited in its ability to handle video services. In sum, the architecture of the decoder of FIG. 1 has only limited flexibility and is specific to a limited configuration of user equipment.
In copending U.S. application Ser. No. 07/970,918 filed Nov. 2, 1992, entitled "System and Method for Multiplexing a Plurality of Digital Program Services for Transmission to Remote Locations," now U.S. Pat. No. 5,319,707 there is described another system, this for Multiplexing a plurality of digital program services comprising a collection of, for example, video, audio, teletext, closed-captioning and "other data" services. According to the disclosed scheme, a plurality of subframe data streams are generated, each having a transport layer region and a program data region. These subframe data streams are then multiplexed together into superframes having a transport layer region and a subframe data region.
As shown in FIG. 2, a decoder 36 is provided at each remote location. The decoder 36 receives a multiplex data stream and extracts a superframe map from each incoming superframe. With the superframe map, the decoder is able to extract the individual subframes from each superframe, thereby recovering each subframe data stream from the multiplex data stream. From a selected subframe data stream, the decoder extracts the subframe multiplex map from each successive subframe in that subframe data stream in order to determine the location of the program multiplex control packet within each subframe. With the program multiplex control packets, the decoder is able to determine which portion of the program data region of each subframe is allocated to a selected program. In this manner, the decoder is then able to extract the selected program. The decoder 36 of FIG. 2 is capable of handling a limited number of video and audio services, as depicted by the drawing.
The decoders shown in FIGS. 1 and 2 thus both exhibit highly structured architectures which allow only for a limited arrangement of services to be received by the subscriber. While these disclosed transmission systems permit a variety of services to be transmitted over various media to remote locations, there remains a need to provide yet other alternative arrangements more particularly adapted to the wide variety of services that may be offered over various media and permit the end user at the remote location greater flexibility over the data content the user is ultimately enabled to receive. Moreover, such a system should be able to be easily adapted to transmit an increasing number of different services in an increasingly efficient manner, for example, utilizing the same or less bandwidth.
Since such services as high definition color television services, so-called "surround-sound" digital audio services, interactive transactional service for home-shopping, reservations, first-run as well as classic movie programming, software delivery, interactive games, alarm services, energy management and such all involve different bandwidths, data formats and such, there remains a need for flexibility in the overall structure provided for transmitting such services. Moreover, a user should not be presented with an overwhelming number of choices, but should be able, in a user-friendly manner, to select only those services which he is capable of receiving or wants to receive. Ideally, the user should be able to have access to an infinite variety of data services, selectable as he chooses, so that he may, for example, watch a first run movie in so-called high definition format accompanied by a "surround-sound" audio in the language of his choice and, at the same time, receive a facsimile or voice communication over the same media. If the user is equipment-limited, for example, to a standard resolution television and a telephone set, the user should be able to fashion the delivery of services to he equipment he owns. Thus, there remains a need for a highly flexible, expandable architecture of a decoder adaptable to receive different services.